JPH0224625A - Production of oriented film for liquid crystal - Google Patents

Abstract

PURPOSE:To increase the pretilt angle of liquid crystal molecules and to improve surface uniformity and contrast by disposing a substrate having a resin layer at a desired angle in the field of parallel magnetic lines of force, exposing ferromagnetic material powder to this field, accelerating and moving particles so as to collide against the surface of the resin layer and removing the magnetic material powder. CONSTITUTION:A polyimide resin and a polyamic resin which are adjusted in viscosity by using a solvent are respectively spin-coated on a glass substrate and are heat-treated at a prescribed temp. The substrate on which a magnetic layer 4 is deposited is then inclined and disposed to the bottom end of a coil 2 by using a device consisting of a copper coil 1 and a DC power source 5 and magnetic powder is dropped from the upper part of the coil 1 toward the coil 1. After the particles of the magnetic powder are brought into collision against the resin layer 4 in such a manner, two sheets of the substrates subjected to the collision are used and the resin layers 4 are disposed to face each other via a prescribed gap. The nematic liquid crystal is packed into this gap. The pretilt angle of the liquid crystal molecules is increased by the magnetic field if the oriented film is formed in such a manner and, therefore the display characteristics of the liquid crystal are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing an alignment film for liquid crystal molecules made of a polymer resin.

Prior Art 7 & Crystal molecule alignment films are essential for liquid crystal displays.

As the alignment film, an inorganic obliquely deposited film, a rubbed organic resin film, etc. are used (for example, 739 and Applications of Liquid Crystal Electronics, edited by Akio Sasaki).

Problems to be Solved by the Invention However, the problem with obliquely deposited inorganic films is that the equipment is relatively expensive and the process cost is high because it is a vacuum process.

In general, rubbing methods are often used in industry, but in a mode where liquid crystal molecules have a large twist angle, ie, super twisted nematic mode, light rubbing pressure and high density rubbing are required. Strict management is required to achieve this condition.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention sets a substrate having a resin layer in a field of almost parallel magnetic lines of force so as to form a desired angle with respect to the lines of magnetic force, The ferromagnetic powder is exposed to this field, and the ferromagnetic powder particles are accelerated and interlocked in a substantially fixed direction by the magnetic lines of force, collide with the surface of the resin layer, and then the ferromagnetic powder is removed. The present invention provides a method for manufacturing a liquid crystal alignment film.

Note that the acceleration and interlocking of the ferromagnetic powder particles and the collision with the surface of the resin layer are performed in a vacuum, in a gas such as air, in water,
A mixture of Daiflon and methanol may also be used. The present invention
Regardless of the atmosphere.

The invention also reveals that substantially parallel magnetic field lines are advantageously generated by electromagnets using superconducting coils.

In order to align the working liquid crystal molecules, it is necessary to align the liquid crystal molecules at the vessel wall interface. For this purpose, an alignment film is usually provided at the interface. It is understood that a certain order is required on the surface of the alignment film. This order may be caused by the groups that interact with liquid crystal molecules being regularly arranged, or by having a regular uneven shape, which results in a decrease in free energy due to the volume exclusion effect, which exerts an alignment regulating force on liquid crystal molecules. It is believed that there may be charges. It is considered that the present invention places some emphasis on the latter orientation mechanism.

The method according to the invention does not require a vacuum and, in this respect, the equipment costs are low.

In addition, in conventional rubbing of a resin film with fibers, etc., if the shake/tilt of the nematic liquid crystal molecules is to be raised slightly from the horizontal, very delicate condition settings and selection of the resin film material are required. The present invention is capable of controlling the strength of parallel magnetic lines of force, their direction with respect to the substrate, the strength of magnetization of ferromagnetic powder, the strength of spontaneous magnetization in some cases, the weight and shape of ferromagnetic powder, and, if necessary, controlling the magnetic field. The intensity is oscillated over time to control the density, depth, and shape of the unevenness on the surface of the resin film, resulting in an effective effect. In this way, even when trying to make the shake/tilt of the nematic liquid crystal molecules slightly higher than the horizontal, the shake/tilt angle can be made larger than before, reproducibility is improved, and the degree of freedom in selecting resin materials is increased. Ta. Further, the magnetic field may be a direct current magnetic field, or an intermittent magnetic field may be better in some cases.

One of the desirable conditions for embodying the present invention is a strong Mi
It is about giving a place. In this respect, it makes sense to use electromagnets using superconducting coils. Of course, currently it is necessary to cool with liquid helium, but if a superconducting coil that can be used at room temperature or liquid nitrogen temperature becomes a reality, the value of the present invention will be great. That is, a strong magnetic field can be obtained with a compact device.

Example An embodiment of the present invention will be described below.

In this example, polyimide resin (solvent type) was used as the resin.
, polyamic acid resin (solvent type) was used. The polyimide resin is used for low pretilt angles for nematic liquid crystals, and the resin originally contains polyimide oligomers. Even polyamic acid resins can be imidized by a predetermined heat treatment, and in this example, a heat treatment capable of imidization was performed.

First, the viscosity of polyimide resin and polyamic acid resin was adjusted using a solvent, and the mixture was spun and coated onto a glass substrate using a spinner. This was heat-treated at a predetermined temperature.

As the ferromagnetic powder, commercially available metal magnetic powder was used as well as commercially available iron oxide magnetic powder.

A small device was created. A schematic diagram of this device is shown in the figure.

In the figure, l is a copper coil, 2 is a magnetic powder, 3 is a substrate, and 4
5 is a resin layer, and 5 is a DC power source.

In addition, the substrate was placed at a desired angle near the ball piece of an electromagnet having a superconducting coil, and the magnetic powder was accelerated from a desired distance and collided with the resin surface.

Substrates having polyimide resin films, substrates having polyamic acid resin films, and substrates that have been bombarded with magnetic powder particles under the same conditions are placed in a normal manner in a predetermined direction while maintaining a predetermined gap. Pasted together. In this case, the resin film was oriented toward the void.

When this gap was filled with 7Mateink liquid crystal, the glass substrate wall was almost aligned in the direction of the applied magnetic field lines.
It was confirmed that the liquid crystal molecules were oriented.

When we measured the pre-tilt angle of the liquid crystal molecules using the magnetic field method, we found that it was several times as large as when using the same resin film and rubbing using the conventional method. This result has conventionally been difficult to obtain with alignment films using resin films. In addition, it was more desirable to intermittent the magnetic field by instantaneously discharging the charge stored in the capacitor.

These results significantly improved the uniformity and contrast of the liquid crystal display compared to the conventional friction method.

When using electromagnets with superconducting coils, the local liquid crystal display characteristics are even better.

Slightly better results are obtained when the atmosphere in which the magnetic powder particles collide is in a vacuum rather than in the air. The atmosphere is
When mixed with methanol or water, compared to when in air,
The results were somewhat poor.

However, there was less scattering of the magnetic powder, and the process was easier to manage.

Effects of the Invention The present invention provides a method for obtaining a resin film for liquid crystal molecule alignment, and can be used for purposes other than liquid crystal display devices.
It has great industrial value.

[Brief explanation of the drawing]

The figure is a schematic diagram of an apparatus for colliding magnetic powder onto a substrate. ■... Copper coil, 2... Magnetic powder, 3.
Old... board, 4... resin layer, 5... DC power supply.

Claims (2)

[Claims] (1) A substrate having a resin layer is set in a field of almost parallel magnetic lines of force at a desired angle to the lines of magnetic force, and ferromagnetic powder is exposed to this field, and the lines of magnetic force cause the ferromagnetic powder to move in an almost fixed direction. A method for producing an alignment film for a liquid crystal, characterized in that particles of ferromagnetic powder are accelerated and interlocked to collide with the surface of the resin layer, and then the ferromagnetic powder is removed. (2) Claim (1) characterized in that the substantially parallel lines of magnetic force are generated by an electromagnet using a superconducting coil.
The method for manufacturing the alignment film for liquid crystal described.